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TOPIC: Evolution of the atmosphere


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Great Oxidation Event
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An international team of geologists may have uncovered the answer to an age-old question - an ice-age-old question, that is. It appears that Earth's earliest ice age may have been due to the rise of oxygen in Earth's atmosphere, which consumed atmospheric greenhouse gases and chilled the earth.
Scientists from the University of Maryland, including post-doctoral fellows Boswell Wing and Sang-Tae Kim, graduate student Margaret Baker, and professors Alan J. Kaufman and James Farquhar, along with colleagues in Germany, South Africa, Canada and the United States, uncovered evidence that the oxygenation of Earth's atmosphere - generally known as the Great Oxygenation Event - coincided with the first widespread ice age on the planet.

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The confluence of the right conditions have helped the earth to generate life as we know it. A change in just one of the ingredients and life itself may have been impossible. One such ingredient is oxygen in the atmosphere, which has made possible life that revolves around burning carbon for energy.
A group of scientists has reported a link between the atmosphere's oxygen supply and fall of nickel levels in the oceans 2.4 billion years ago.

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RE: Evolution of the atmosphere
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Sedimentary rocks created more than 2.4 billion years ago sometimes have an unusual sulphur isotope composition thought to be caused by the action of ultra violet light on volcanically produced sulphur dioxide in an oxygen poor atmosphere. Now a team of geochemists can show an alternative origin for this isotopic composition that may point to an early, oxygen-rich atmosphere.

"The significance of this finding is that an abnormal isotope fractionation (of sulphur) may not be linked to the atmosphere at all. The strongest evidence for an oxygen poor atmosphere 2.4 billion years ago is now brought into question" - Yumiko Watanabe, research associate, Penn State.

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Great Oxidation Event
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The Earth's original atmosphere held very little oxygen. This began to change around 2.4 billion years ago when oxygen levels increased dramatically during what scientists call the 'Great Oxidation Event.' The cause of this event has puzzled scientists, but researchers writing in today's Nature have found indications in ancient sedimentary rocks that it may have been linked to a drop in the level of dissolved nickel in seawater.

"The Great Oxidation Event is what irreversibly changed surface environments on Earth and ultimately made advanced life possible. It was a major turning point in the evolution of our planet, and we are getting closer to understanding how it occurred" - research team member Dominic Papineau of the Carnegie Institution's Geophysical Laboratory.

The researchers, led by Kurt Konhauser of the University of Alberta in Edmonton, analysed the trace element composition of sedimentary rocks known as banded-iron formations, or BIFs, from dozens of different localities around the world, ranging in age from 3,800 to 550 million years. Banded iron formations are unique, water-laid deposits often found in extremely old rock strata that formed before the atmosphere or oceans contained abundant oxygen. As their name implies, they are made of alternating bands of iron and silicate minerals. They also contain minor amounts of nickel and other trace elements.

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RE: Evolution of the atmosphere
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A Tale of Two Gases: The Biogeochemistry of 02 and N20
The history of oxygen on Earth

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The land was devoid of plants and animals, but there was life in the ocean, mainly in the form of plankton, sea sponges, and trilobites. Most of the early ancestors of the plants and animals we know today existed during the Cambrian, but life wasn't very diverse.
Then, during the Ordovician period, which began around 490 million years ago, many new species sprang into being. The first coral reefs formed during that time, and the first true fish swam among them. New plants evolved and began colonizing land.

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470millonY
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The Cambrian is a major division of the geologic timescale that begins about 542 1.0 Ma (million years ago) at the end of the Proterozoic eon and ended about 488.3 1.7 Ma with the beginning of the Ordovician period (ICS, 2004).

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-- Edited by Blobrana at 23:57, 2007-11-01

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Ohio State University geologists and their colleagues have uncovered evidence of when Earth may have first supported an oxygen-rich atmosphere similar to the one we breathe today.
The study suggests that upheavals in the earth's crust initiated a kind of reverse-greenhouse effect 500 million years ago that cooled the world's oceans, spawned giant plankton blooms, and sent a burst of oxygen into the atmosphere.
That oxygen may have helped trigger one of the largest growths of biodiversity in Earth's history.
Matthew Saltzman, associate professor of earth sciences at Ohio State, reported the findings Sunday at the meeting of the Geological Society of America in Denver .
For a decade, he and his team have been assembling evidence of climate change that occurred 500 million years ago, during the late Cambrian period. They measured the amounts of different chemicals in rock cores taken from around the world, to piece together a complex chain of events from the period.
Their latest measurements, taken in cores from the central United States and the Australian outback, revealed new evidence of a geologic event called the Steptoean Positive Carbon Isotope Excursion (SPICE).
Amounts of carbon and sulphur in the rocks suggest that the event dramatically cooled Earth's climate over two million years -- a very short time by geologic standards. Before the event, the Earth was a hothouse, with up to 20 times more carbon dioxide in the atmosphere compared to the present day. Afterward, the planet had cooled and the carbon dioxide had been replaced with oxygen. The climate and atmospheric composition would have been similar to today.

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University of Alberta researchers have helped to uncover evidence that oxygen existed on Earth millions of years earlier than believed, a finding that casts new light on how the planet developed conditions to support life.
As part of an international team of scientists, geologist Robert Creaser and PhD student Brian Kendall contributed to the discovery by analysing and dating ancient shale taken from the Hamersely Basin in western Australia.


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